Sideritialliset

Sideritialliset refers to a measurement of time based on the apparent motion of the stars. Unlike solar time, which is based on the Sun's position in the sky, sideritial time is determined by the Earth's rotation relative to distant stars. A sideritial day is slightly shorter than a solar day, approximately 23 hours, 56 minutes, and 4 seconds. This difference arises because as the Earth orbits the Sun, it must rotate a little extra each day to bring the same star back to the same position in the sky.

Astronomers utilize sideritial time for precise observations and tracking of celestial objects. Because the stars appear to move at a more constant rate throughout the year compared to the Sun, sideritial time provides a stable reference frame for cataloging and predicting the positions of stars, galaxies, and other astronomical phenomena. Sidereal time is crucial for operating telescopes that track celestial objects as the Earth rotates, ensuring the object remains centered in the field of view. It is calculated using Greenwich Mean Sidereal Time (GMST) at the prime meridian and then adjusted for local longitude to determine Local Mean Sidereal Time (LMST).